1. Field of the Invention
This invention relates in general to drilling and production of oil and gas wells and, in particular, to a tubular connector having an elliptically undercut shoulder.
2. Brief Description of Related Art
Offshore hydrocarbon wells often contain one or more casing strings of large diameter pipe, such as 16 inches or greater in diameter. Production risers extending from subsea well equipment to the surface are also made-up of fairly large diameter pipes. The joints of pipe, whether in a casing string or production riser string, are connected together by threaded connections. A typical threaded connection has internal threads on a conical portion of a box that engage external threads on a pin. Normally, the pin has an external shoulder at the base of the threads that is engaged by the rim of the box when made up.
Many prior art riser or tubular member joint connectors use pin and box type connectors. These pin and box type connecters have a first tubular member with a larger diameter portion on an end, the box, and a second tubular member with a smaller diameter portion on an end, the pin. The pin inserts into the box end to join the two tubular members by any suitable means such as threading of the pin into the box, cammed engagement of grooves, or the like. Generally, the tubular members transition to the larger diameter connector portions across a fairly short distance, often having angles that are substantially close to right angles between the connector and the tubing. These right angle transitions provide a substantially planar surface that is perpendicular to an axis of the tubular for engagement with a tubing elevator for manipulation of the tubular member. Unfortunately, these transition areas are often subject to high stress that may cause early failure of the connector. Attempts have been made to reduce this stress by increasing the length of the transition; however, a longer transition generally requires an increase in the clamping diameter of elevator as the thickness of the tubular at the engagement point of the elevator will increase by increasing the transition. A longer transition requires use of specialty elevators to accommodate the thicker tubing diameter.